Major Hurricanes & Climate Change
Written By: Marjahn Finlayson, Founder of The Fin Forecast
Hurricane Melissa
Hurricane Melissa's intensity (which went up to category 5 strength) has been influenced by climate change. When it comes to hurricane development, we look three key environmental components: sea surface temperature above 26ºC, atmospheric moisture in the mid-troposphere, and low vertical wind shear (i.e. a change in wind speed or direction with a change in altitude).
Despite vertical wind shear being relatively high, along with high sea surface temperatures and high mid-tropospheric moisture, Melissa went from a tropical storm to a Category 5 in one week. This is partially due to the very slow translational speed on this storm in the Caribbean Sea during this week, also high ocean heat content (heat energy down to ~2000m in the ocean) and low sea surface salinity (less than 35 PSUs) in the Caribbean Sea from last week to now. These oceanic components have been studied to show they also influence rapid intensification of tropical cyclones in the Atlantic Ocean.
What does that have to do with with climate change?
As we know, climate change is the long term atmospheric difference over a geographical region. The climate (long term atmospheric conditions, e.g. warm summers in The Bahamas) changes as a result of what is known as global warming, where the planet's heat energy surrounding it has increased since the mid 1800s. This is because emissions known as greenhouse gases.
Before anthropogenic (human-influenced) emissions began in the 1850s, the greenhouse gases were a thin layer of gases over the Earth that acted like a blanket or greenhouse, meant to insulate heat for the planet because we all need heat to live. In the 1800s, at the advent of the Industrial Period, scientists found that carbon emissions were having an effect on the atmosphere and they predicted over a long period that this gas would impact heating. And they were right, carbon dioxide, methane, nitrous oxide and even water vapour are all greenhouse gases and that been increased in the atmosphere, leading to a stronger greenhouse effect on Earth which has trapped more heat than in previous centuries. More heat means global warming which leads to changes in the climate.
The Ocean’s Role
The ocean is particularly impacted by climate change because it is a large sink for carbon and heat. More carbon in the ocean is grounds for ocean acidification and more heat means hotter waters at surface, intermediate and deep levels. This also can effect ocean mixing and increase stratification, which in turn may impact how water masses move! Hot ocean molecules also expand which leads to sea level rise!
Sea surface salinity can be impacted by increased evaporation with the water cycle because of climate change, and increased evaporation creates conditions where sea surfaces are more saline which can impede tropical cyclone development. BUT because water masses aren't stationary, it may not mean much and more saline surfaces along with more stratified ocean may simply affect ocean circulation in the deep waters.
What we do know:
Hotter air temperatures mean more heat sinks in the ocean and more moisture in the atmosphere.
Hotter ocean temperatures mean high ocean heat content and sea surface temperatures, increasing chances of hurricane development and growth.
More moisture in the atmosphere can mean heavier rainfall with most tropical cyclones due to climate change. Along with sea level rise, more rain means more possibilities for flooding.
Hotter oceans means water molecules expand and add to sea level rise (along with melting ice glaciers).
Takeaway message
Hurricanes are rapidly intensifying due to environmental changes that impacted by climate change. Climate change is expected to continue into the next century due to past and current greenhouse gas emissions. Small Island Developing States, like those in the Caribbean, are most impacted by climate change disasters. Hurricane Melissa is one example of how a changing climate continues to make formerly rare occurrences (dangerous major hurricanes) new normals that we see almost every year.